Pretty damn fine, and it's good you wrapped it up fairly quickly as a oneshot. While I enjoy the 'what-if Aizen didn't have a deus-ex-machina butterfly form' scenario, I think the funniest part of the story was Gin's comment at the end that Ichigo is 'very creepy'.

And that's the way it should've ended. Except for maybe having Ichigo still being normal. Otherwise that's just so much wasted potential. But his indifferent composure was a great addition to the scene. I always thought that Gin should've just put as much venom into that bastards body as possible, until nothing but the Hogyoku was left.

. . . And THAT, is what Gin SHOULD have done. Great begining, I love it! Your writing style is very well developed, considering this being your first fic. Congrats! If you decide to continue this and make it into a multi chapter story I wouldn't complain! hmmmmm. . . If this chapter ended with Gin following Ichigo, would Ichigo return to the shinigami or would he go and find his sisters? (They were never mentioned in the whole Decide arc I believe) would the shinigami accept both of them? one who betrayed them (even for a good cause) and the other who can kill them with a single brush of skin? hmmm. . . oh the possibilities. . . I hope you write more stories, your writing style is like a breath of fresh air compared to some other people's writing. Thanks!

But I guess it wouldn't properly be Bleach if Kubo didn't fanspasm all over Ichigo's everything and make him the hero. Even though Urahara was the one that actually took Aizen out after Ichigo looked pretty and shiny for a while. Aha, but I think I like this version a bit better.

I'm kind of skeptical on the carnage part, though. I always saw Gin as a quick and simple attacker, like how a snake strikes lightening fast and then retreats. But I suppose he could have that blood and gore side of him too.

The part where Gin mentions that Ichigo is creepy - creeps me out too. If Gin(one of the creepiest character in Bleach in my opinion) thinks Ichigo's creepy...!

Uaah! This sounds like it could be the start of something *very* interesting. It's also well written with a better grasp of the language it's written in than a lot I've seen (or some I've produced, for that matter).